The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Gelled liquid hydrocarbon fluids have been utilized in a variety of treatments for subterranean formations penetrated by well bores, including stimulation activities such as fracturing, gravel packing, sand control and the like. Such hydrocarbon fluids must have a sufficiently high viscosity to generate a fracture of sufficient dimensions and also to carry the proppant particles to the wellbore and to the fracture. Oil-based treatment fluids, i.e., free of water or having an external organic phase, are used to treat formations having sensitivity to water or which may suffer permeability reduction or damage when exposed to aqueous fluids.
Ideally, in fracturing applications, additives are designed to provide high viscosity to the frac fluid at the time of pumping and lower the viscosity after the proppant is placed in the fracture by breaking the fluid. For water-base fluids, reducing agents and oxygen scavengers are often used as stabilizers to maximize the initial viscosity of the fluid. Oxidizing agents are generally used to break the fluid. As both the additives (stabilizers and breakers) are added together to the fluid, they compete with each other making each one less efficient. For example, live breakers can start breaking the fluid as soon as it is mixed in the fluid, and no delay in breaking is inherent in these systems. Thus, there is no single additive which helps with both boosting the initial viscosity and as a breaker at the end of pumping. Similar stabilization and breaking issues also exist for oil-base fracturing fluids.
Viscoelastic surfactants (VES) are known to boost the viscosity of hydrocarbon based gels from US20050233911 and U.S. Ser. No. 12/433,076. U.S. Ser. No. 12/433,076 also discloses that base precursors such as ureas and substituted ureas, cyanates, alkylamines and certain alkanolamines and quaternary ammonium salts, among others, can be used as encapsulated alkaline pH modifiers to cause emulsion destabilization. On the other hand, U.S. Pat. No. 6,232,274 discloses that urea, guanidine hydrochloride, urethane and the like are used to increase the viscosity of VES fluids in aqueous systems. In phosphate-gelled oil systems, U.S. Pat. No. 4,919,209 discloses sodium carbonate, sodium bicarbonate, sodium acetate, p-nitrobenzoic acid, triethanolamine, sodium acetate, sodium bicarbonate, calcium oxide, calcium hydroxide and the like are used as breakers at heavy loading. For delayed breaking in gelled oils, U.S. Pat. No. 5,948,735 discloses using particulated urea, metal hydroxides and carbonates encapsulated with oil-degradable materials, such as rubber.
A single additive that could be used as both a viscosity booster and breaker in the same system would greatly simplify oil-based gel preparation and use, among other advantages.